Backrests of known chairs commonly have three kinds: 1. a metal backrest made of metal; 2. a plastic backrest made of plastic; 3. a wood backrest made by wood. The metal backrest has the disadvantages of high heat conductivity and bad decoration, which makes the metal backrest not favorable for users. The plastic backrest has the disadvantages of low heat conductivity and bad decoration, which makes the plastic backrest not favorable for users. Wood backrests have moderate heat conductivity and good decoration, which makes the wood backrest favorable for users. The wood backrest has disadvantages as follows: 1. The wood backrest has an inconvenient connection with metal backrest pole and has low connection intensity; 2. The wood backrest requires a connection part for connecting with the backrest pole, which will waste much wood.